A Review on Use of Emulsified Acids for Matrix Acidizing in Carbonate Reservoirs

摘要

Almost 60% of oil and 40% of gas reserves worldwide are contained in carbonate reservoirs where acidizing stimulation is more challenging compared to sandstone reservoirs. The high reactivity rate of the acid with carbonate causes hard controlling of the direction of acid in the formation, from one hand, and fast consumption of the acid, from the other hand. To solve this problem, the reaction between the acid and rock needs to be retarded to elongate the life and strength of the acid, and hence, allow deeper penetration. One of the techniques used to accomplish that is by utilizing emulsified acid, which is widely considered as a major source for successful matrix acidizing operations for more than half a century. Besides slowing down the reactivity, the emulsified acid introduces other advantages which collectively further improves the overall benefits of the matrix acidizing process and increase its potentiality for application. Examples of such advantages are corrosion inhibition of the well equipment and flow catering to low permeable zones. This paper attempts to review the various kinds of emulsified acids that are used for matrix acidizing of carbonate formations. The paper is trying to trace out the innovative solutions that have, gradually, been applied for enhancing the performance of emulsified acids for a variety of conditions, especially under high temperature. In addition, the paper also discusses the conditions required for a successful synthesis of stable emulsions taking into account the recent environmental concerns raised towards the application of diesel based emulsified acid systems.